Style Sheets: CSS, XSL, CSS-OM (Bert Bos)
May 24, 1999
Bert Bos spoke about trends in the W3C's stylesheet efforts. A major push toward modularization will
take place during the next 12 months.
- CSS-OM (Object Model)- access to CSS from within programs (a la DOM for HTML and XML)
- CSS modularization and user-agent profiles
- XSL modularization, initial recommendations
- CSS2/CSS3 test suite
(note the CSS1 Test Suite and
CSS2 Validation Service)
Modularization will include modules targeted for specific device types.
I believe Bert said that CSS typographic and speech properties will be submitted to an ISO group for standardization.
CSS (Cascading Style Sheets)
permits rendering without resorting to tables. Number of bytes transmitted is smaller
than using numerous font tags, etc. Special Webfonts can be downloaded. The term cascade refers to the combining
of what the author intends for style with that of the user and, to some extent, browser defaults.
CSS can be used with either HTML or XML.
Bert listed support tools from W3C for CSS,
including Amaya, a direct manipulation editor/browser.
XSL (Extensible Stylesheet Language)
builds a separate display structure by extracting information from the source (XML) document.
XSL can only be used with XML.
With regard to XSL tools, Bert predicted there would be many after XSL becomes a full fledged W3C
Recommendation. In the meantime, he mentioned that XSL tools from
InDelv,
ArborText,
Microsoft,
Inso Corp. and
James Tauber's FOP
are really only experimental at this point.
Bert predicted that XSLT will be finalized in the summer of 1999 and XSL-FO in the fall of 1999.
Both specifications are considered "feature complete" by the XSL Working Group although syntax
and element names are likely to change over the next few months.
His slides include a very helpful diagram that shows the
interplay of HTML, XML, CSS, XSLT, and XSL-FO.
XSL has about 50 Formatting Objects defined, such as block, inline-sequence, and table-row.
(The names are hyphenated as are CSS properties.)
An XSL Formatting Object is an area of the display device that has certain properties that describe
the appearance of the area, plus content (text, image, or other FO's). Bos compares this to HTML:
"FO = element + properties - element-type - attributes"
CSS Object Model (CSS-OM) is the new effort to create an object model for CSS analogous to the DOM.
CSS-OM will permit accessing rules, properties, values, modules, from within a program,
inserting rules, changing values, removing properties, and more.
While CSS level 1 and 2 provide modularization for the style designer, CSS level 3
will provide modularization
for implementers. This will include more precise descriptions of
devices and style information for non-text objects, such as SVG, MathML, and SMIL.
See Bert Bos's W3C Track talk for more details.
I did not attend his other talk,
Towards CSS Modularization,
on Developer's Day. The slides indicate a tentative date of December 1999. They also state
the goals of CSS Modularization
and the projected modules.)
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